Surgical sterilization is currently the most common method of contraception among married couples in the United States [1]. Male sterilization (vasectomy) has a higher success rate, lower morbidity and mortality rate, is less expensive, and easier to perform than female sterilization (tubal ligation) [1-3]. Despite these advantages, however, female sterilization is more commonly performed. Fear of complications related to surgery was frequently cited as the primary reason for a couple choosing tubal ligation instead of vasectomy [1,2,4]. In the U.S., for example, there are approximately 500,000 vasectomies and 1 million tubal ligations performed each year [5]. Worldwide, approximately 40 million men have had a vasectomy [6]. While there have been no reported cases of vasectomy-related deaths in the U.S. [7, 8], there are 10-20 deaths each year due to tubal ligation. Worldwide, these numbers are even greater [8]. Complication rates of vasectomy range from 1-6% and include sterilization failure, hematoma, infection, sperm granuloma, and epididymitis [9-11]. However, several studies have reported much higher rates of infection (12-38%) which may be due primarily to the experience of the physician performing the procedure [5].
During conventional surgical vasectomy, the vas deferens is separated from the spermatic cord vessels and manipulated to a superficial position under the scrotal skin. A needle is used to inject local anesthesia around the vas, producing a vasal nerve block. Then 1-cm-long incisions are made through the vas sheath until the vas is exposed. The vas is delivered and the deferential artery, veins, and nerves are dissected free of the vas and spared. A 1-cm-long vas segment is then removed and the ends of the vas are occluded using thermal cautery, followed by the placement of hemoclips [5].
Although conventional vasectomy is a simple, inexpensive procedure with minimal morbidity, there are several reasons for exploring a noninvasive approach to male sterilization. An incision-less and puncture-less method of male sterilization would eliminate surgery and the associated risks of infection, bleeding, and scrotal pain. This may lead to greater acceptance of vasectomy by men, reducing the morbidity, mortality, and cost associated with tubal ligation. Therefore, there is a clear need for safer, less invasive method to perform vasectomies.
In recent years, the “no-scalpel” vasectomy technique has been developed to minimize complications associated with incision during the procedure [12]. This method eliminates the use of the scalpel, results in fewer hematomas and infections, and leaves a smaller wound than conventional methods [5]. The success of this method is proven by a complete reversal in the ratio of male to female sterilizations, now 3 to 1, in the Szechuan province of China [4]. However, despite the name “no-scalpel-vasectomy”, this procedure still requires a puncture through the skin and does not completely eliminate the possibility of bleeding, infection, and scrotal pain. A “no-scalpel” vasectomy technique has also been disclosed in U.S. Pat. No. 4,920,982 to Goldstein; however, this procedure requires a step of inserting a sharp-tipped needle into the scrotum and through a wall of the vas deferens. This procedure too requires a puncture through the skin, thereby exposing the vas deferens, and it does not completely eliminate the possibility of bleeding, infection, and scrotal pain.
A percutaneous approach to vasectomy has also been performed in over 500,000 men using chemical ablation with cyanoacrylate and phenol [13-15]. A needle is placed into the lumen of the vas using a series of tests involving dye injections for confirmation. Although pharmacologic tests of the cyanoacylate-phenol mixture have demonstrated no toxicity, these chemicals are not approved for use in the U.S. Another concern with this method is the great skill involved with gaining percutaneous access to the 300-μm-diameter lumen of the vas deferens.
Thermal methods of vas occlusion have also been studied for producing more reliable permanent vas occlusion. Some of these studies have suggested that thermal destruction of the vas luminal integrity provides more successful prevention of recanalization of the vas than does suture ligation during wound healing, with failure rates decreasing from 1-6% to 0.24% [9,16]. As a result, it is now common for physicians to cauterize the cut ends of the vas as an alternative to ligation. There is also evidence that more uniform thermal necrosis of the vas lumen with hot wire rather than superficial lumen destruction using electrocautery provides more successful results [17]. These studies used thermal techniques in either a minimally invasive surgical or percutaneous approach to vasectomy [9, 17, 18].
The use of ultrasound as a noninvasive technique for vas occlusion has been studied. Ultrasound, however, has many disadvantages, including but not limited to the requirement of a coupling medium, which may obstruct the urologist's field-of-view. Further, focused ultrasound typically creates acorn-shaped lesions with a higher depth-to-with ratio, which is more likely to damage tissue structures immediately surrounding the vas.